JP7295957B2 - Dye-sensitized solar cell - Google Patents

Description

The present disclosure relates to dye-sensitized solar cells.

Solar cells are roughly classified into three types, silicon-based, compound-based, and organic-based, according to their materials. Silicon-based solar cells have high conversion efficiency, and solar cells using polysilicon are most widely used for power generation using sunlight. One of the organic cells is a dye-sensitized solar cell (hereinafter sometimes abbreviated as “DSC”). DSCs are inferior to silicon-based semiconductors in terms of conversion efficiency, but have the advantage of lower manufacturing costs than silicon-based or compound-based inorganic semiconductors, and have been attracting attention in recent years. In addition, DSCs have the advantage of obtaining higher power generation efficiency than silicon-based ones in a low-illuminance environment, and this point is also attracting attention.

Patent Documents 1 to 3 disclose dye-sensitized solar cells having electrolyte solutions containing pyrazole compounds. By including the pyrazole-based compound in the electrolyte solution, it is possible to suppress a reverse current that may flow independently of light irradiation and improve the open-circuit voltage of the DSC.

Japanese Patent Application Laid-Open No. 2003-331936 JP-A-2004-47229 JP-A-2005-216490

According to the study of the present inventors, the open-circuit voltage Voc and the short-circuit current Jsc decrease when the DSC is heated to about 80° or more. One of the reasons for this is that the heat resistance of pyrazole compounds cannot be said to be good. Therefore, when the DSC reaches a high temperature, the mere inclusion of the pyrazole-based compound in the electrolyte solution is not sufficient to suppress the decrease in the open-circuit voltage and the short-circuit current. By improving the heat resistance of the DSC, that is, by improving the heat resistance, an effect of suppressing the decrease in the open-circuit voltage and the short-circuit current is expected.

The present disclosure has been made in view of the above problems, and an object thereof is to provide a dye-sensitized solar cell capable of appropriately suppressing a decrease in open-circuit voltage Voc and short-circuit current Jsc.

In order to solve the above problems, a dye-sensitized solar cell according to an aspect of the present disclosure includes a first electrode having a porous semiconductor layer containing first metal oxide particles and supporting a dye; and a porous insulating layer provided between the second electrode serving as a counter electrode and the first electrode and the second electrode, holding an electrolytic solution containing a redox couple and a pyrazole compound, and a second metal oxidation a porous insulating layer containing particles.

An exemplary embodiment of the present invention provides a novel dye-sensitized solar cell capable of appropriately suppressing a decrease in open-circuit voltage Voc and short-circuit current Jsc.

1 is a schematic cross-sectional view of a DSC 100 according to this embodiment; FIG. FIG. 4 is a schematic cross-sectional view of a DSC 200 according to a comparative example; FIG. 4 is a diagram for explaining how a pyrazole-based compound is unevenly distributed near the surface of a counter electrode conductive layer 28. FIG.

Before describing the embodiments of the present invention, the findings of the inventors, which formed the basis of the present invention, will be described with reference to FIG.

FIG. 3 shows a schematic cross-section of a DSC 200 having a conventional sandwich-type cell structure. The DSC 200 has a translucent substrate 12 , a transparent conductive layer 14 formed on the substrate 12 , and a porous semiconductor layer 16 formed on the transparent conductive layer 14 . The porous semiconductor layer 16 has fine semiconductor particles and pores, and carries a dye (not shown). The porous semiconductor layer 16 is made of titanium oxide, for example.

The DSC 200 further includes a translucent substrate 22 , a transparent conductive layer 24 formed on the substrate 22 , and a counter electrode conductive layer 28 formed on the transparent conductive layer 24 . An electrolytic solution (electrolyte solution) 42 is filled between the porous semiconductor layer 16 and the counter conductive layer 28 . The electrolytic solution 42 is sealed in the gap between the substrates 12 and 22 by the sealing portion 52 . The electrolyte 42 contains, for example, I ⁻ and I ₃ ⁻ as mediators (redox pairs). The sealing portion 52 is formed using a photocurable resin or a thermosetting resin. The porous semiconductor layer 16 functions as a positive electrode, and the counter conductive layer 28 functions as a negative electrode. A cell structure in which a positive electrode and a negative electrode are bonded together in this way is generally called a sandwich-type cell structure. The dye-sensitized solar cells disclosed in Patent Documents 1 to 3 have a sandwich type cell structure.

Dye-sensitized solar cells are said to have weak resistance to heat, and in particular, performance drops significantly when tested in accordance with JIS 8938 heat resistance test B-1 (high temperature storage: temperature 85 ± 2 ° C). I have a problem. When the DSC is heated above about 80° C., the redox couple I ₃ ⁻ in the electrolyte is decomposed to produce I ₂ and I ⁻ . I ₂ is adsorbed on the surface of the porous semiconductor layer 16 made of titanium oxide and becomes a current leak source, which lowers the open-circuit voltage Voc and the short-circuit current Jsc.

When a pyrazole-based compound is added to the electrolyte solution of the dye-sensitized solar cells disclosed in Patent Documents 1 to 3, the pyrazole-based compound certainly binds to I ₂ to suppress adsorption to the titanium oxide surface. . This suppresses leakage of electrons from the surface of the porous semiconductor layer to the redox pair I ₃ ⁻ , and as a result, an improvement in the open-circuit voltage Voc is expected.

According to the study of the inventor, the hydrogen element (proton) bound to the nitrogen element at the first position of the pyrazole-based compound is easily desorbed in the electrolytic solution. Therefore, the pyrazole-based compound releases a hydrogen group and becomes negatively charged. Also, in the case of a sandwich-type DSC, the counter electrode tends to be positively charged. Therefore, the pyrazole-based compound, which is negatively charged by liberating the hydrogen group, is attracted to the positively charged counter electrode side shown in the rectangular area 50 in FIG. 3 and is unevenly distributed in the vicinity of the counter electrode. As a result, the concentration of the pyrazole-based compound in the electrolytic solution near the surface of the porous semiconductor layer facing the counter electrode is reduced, and the pyrazole-based compound is less likely to react with I ₂ in the titanium oxide pores.

Thus, in the sandwich-type cell structure, even when a pyrazole-based compound is added to the electrolyte, a sufficient effect of appropriately suppressing current leakage from the surface of the porous semiconductor layer to the redox pair I ₃ ⁻ is exhibited. There is a problem that it is not Furthermore, it cannot be said that the heat resistance of pyrazole compounds is good.

Based on the above findings, the present inventors have found that by stacking a porous insulating layer and a counter electrode conductive layer on a porous semiconductor layer, that is, by adopting a monolithic cell structure, a pyrazole compound is placed near the counter electrode. The inventors have found that the ubiquitous phenomenon can be improved and have completed the present invention.

In a non-limiting exemplary embodiment, the dye-sensitized solar cell of the present invention includes a first electrode having a porous semiconductor layer containing first metal oxide particles and supporting a dye; and a porous insulating layer provided between the first electrode and the second electrode. The porous insulating layer holds an electrolytic solution containing a redox couple and a pyrazole compound, and contains second metal oxide particles. The first electrode includes at least a porous semiconductor layer supporting a dye, and may further include a conductive layer. The first electrode is also called a photoelectrode. A 2nd electrode is an electrode which functions as a counter electrode of a photoelectrode, and may only be called a counter electrode. The counter electrode has at least a counter electrode conductive layer and may further have a catalyst layer. The counter electrode conductive layer may also serve as the catalyst layer.

In a module in which a plurality of dye-sensitized solar cells (sometimes referred to as "unit cells" or simply "cells") are integrated, adjacent cells are electrically connected in series or parallel, for example. At this time, for example, the photoelectrode of one cell is connected to the counter electrode of the other cell by sharing a transparent conductive layer formed on the substrate. A typical example of the cell structure of the dye-sensitized solar cell according to this embodiment is a monolithic integrated structure.

Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially the same configurations may be omitted. This is to avoid unnecessary verbosity in the following description and to facilitate understanding by those skilled in the art. The inventors provide the accompanying drawings and the following description for a full understanding of the invention by those skilled in the art. They are not intended to limit the claimed subject matter. In the following description, identical or similar components are given the same reference numerals. The embodiments described below are merely examples, and various combinations of aspects are possible as long as there is no technical contradiction.

FIG. 1 shows a schematic cross-sectional view of the DSC 100. As shown in FIG. DSC 100 is a DSC with a monolithic cell structure. The DSC 100 includes a transparent substrate 12, a transparent conductive layer 14a formed on the substrate 12, a porous semiconductor layer 16A formed on the transparent conductive layer 14a, and a porous semiconductor layer 16A covering the porous semiconductor layer 16A. It comprises an insulating layer 36A, a transparent conductive layer 14b formed on the substrate 12, a counter electrode conductive layer 28A formed on the porous insulating layer 36A, and a substrate 22 having translucency.

The porous semiconductor layer 16A and the counter electrode conductive layer 28A are arranged so as to include more portions facing each other with the porous insulating layer 36A interposed therebetween. The counter electrode conductive layer 28A is electrically connected to the transparent conductive layer 14b formed on the substrate 12. As shown in FIG. A scribe line 60 is formed on the substrate 12 that electrically separates the transparent conductive layer 14a from the transparent conductive layer 14b. That is, the transparent conductive layers 14 a and 14 b are insulated from each other on the substrate 12 .

The gap between the substrate 12 and the substrate 22 is filled with the electrolytic solution 42 and sealed by the sealing portion 52 . The electrolytic solution 42 permeates the entirety of the porous semiconductor layer 16A, the porous insulating layer 36A and the counter electrode conductive layer 28A. The electrolytic solution 42 contains, for example, I ⁻ and I ₃ ⁻ as a redox pair. The sealing portion 52 is formed using a photocurable resin or a thermosetting resin.

A glass substrate or a flexible film, for example, can be used as the substrates 12 and 22 . However, the substrates 12 and 22 may be formed of a material that substantially transmits light having a wavelength effective for the dye to be described later, and does not necessarily transmit light in all wavelength regions. you don't have to. The thickness of the substrates 12 and 22 is, for example, 0.2 mm or more and 5.0 mm or less. Note that the substrate 22 does not have to be translucent.

As materials for the substrates 12 and 22, substrate materials generally used for solar cells can be widely used. For example, a glass substrate such as soda glass, fused quartz glass, or crystal quartz glass, or a heat-resistant resin plate such as a flexible film can be used. Flexible films such as tetraacetylcellulose (TAC), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate (PA), polyetherimide (PEI), phenoxy resin or Teflon (registered trademark) and the like can be used.

The transparent conductive layers 14a and 14b are generally used in solar cells and formed of a material having conductivity and translucency. As the material, for example, at least one selected from the group consisting of indium tin composite oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO) and zinc oxide (ZnO) can be used. The thickness of the transparent conductive layers 14a and 14b is, for example, 0.02 μm or more and 5.00 μm or less. The electrical resistance of the transparent conductive layers 14a and 14b is preferably as low as possible, for example, 40Ω/□ or less.

The porous semiconductor layer 16A has semiconductor fine particles (first metal oxide particles) 16s and pores 16p, and carries a dye (not shown). The porous semiconductor layer 16A is an aggregate of semiconductor fine particles of titanium oxide, for example, and is porous.

The porous semiconductor layer 16A is made of a photoelectric conversion material. Materials such as titanium oxide, zinc oxide, tin oxide, iron oxide, niobium oxide, cerium oxide, tungsten oxide, barium titanate, strontium titanate, cadmium sulfide, lead sulfide, zinc sulfide, indium phosphide, copper-indium At least one selected from the group consisting of sulfide (CuInS ₂ ), CuAlO ₂ and SrCu ₂ O ₂ can be used. Titanium oxide is preferably used because of its high stability and its large bandgap.

As titanium oxide, for example, various narrowly defined titanium oxides such as anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, metatitanic acid, and orthotitanic acid, titanium hydroxide, hydrous titanium oxide, etc., alone, or They can be mixed and used. Two types of crystalline titanium oxide, anatase type and rutile type, can be in either form depending on the manufacturing method and heat history, but generally crystalline titanium oxide is anatase type. From the viewpoint of dye sensitization, it is preferable to use titanium oxide having a high anatase content, for example, titanium oxide having an anatase content of 80% or more.

The crystal system of the semiconductor may be either single crystal or polycrystal, but polycrystal is preferable from the viewpoint of stability, ease of crystal growth, and manufacturing cost. It is preferable to use microscale semiconductor fine particles. Therefore, it is preferable to use fine particles of titanium oxide as the raw material of the porous semiconductor layer 16A. Fine particles of titanium oxide can be produced, for example, by a liquid phase method such as a hydrothermal synthesis method or a sulfuric acid method, or a method such as a vapor phase method. It can also be produced by high temperature hydrolysis of chloride developed by Degussa.

As the semiconductor microparticles, a mixture of microparticles having two or more types of particle diameters made of the same or different semiconductor compounds may be used. It is believed that semiconductor fine particles with a large particle size contribute to the improvement of the light trapping rate by scattering incident light, and semiconductor fine particles with a small particle size contribute to an increase in the amount of dye adsorption by increasing the number of adsorption points.

When using semiconductor fine particles in which fine particles having different particle diameters are mixed, it is preferable that the ratio of the average particle diameters of the fine particles is 10 times or more. The average particle size of fine particles having a large particle size is, for example, 100 nm or more and 500 nm or less. The average particle size of fine particles having a small particle size is, for example, 5 nm or more and 100 nm or less. When semiconductor fine particles in which different semiconductor compounds are mixed are used, it is effective to reduce the particle size of the semiconductor compound having a strong adsorption action.

The thickness of the porous semiconductor layer 16A is, for example, 0.1 μm or more and 100.0 μm or less. Moreover, the specific surface area of the porous semiconductor layer 16A is preferably, for example, 10 m ² /g or more and 200 m ² /g or less.

As the dye carried on the porous semiconductor layer 16A, one or more of various organic dyes and metal complex dyes having absorption in the visible light region or the infrared light region can be selectively used.

Examples of organic dyes include azo dyes, quinone dyes, quinoneimine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes, porphyrin dyes, and perylene. At least one selected from the group consisting of dyes based on dyes, indigo dyes and naphthalocyanine dyes can be used. The absorption coefficient of an organic dye is generally larger than that of a metal complex dye in which a molecule is coordinated to a transition metal such as ruthenium.

A metal complex dye is composed of a molecule coordinated with a metal. The molecule is, for example, a porphyrin-based dye, a phthalocyanine-based dye, a naphthalocyanine-based dye, or a ruthenium-based dye. Metals include, for example, Cu, Ni, Fe, Co, V, Sn, Si, Ti, Ge, Cr, Zn, Ru, Mg, Al, Pb, Mn, In, Mo, Y, Zr, Nb, Sb, La , W, Pt, TA, Ir, Pd, Os, Ga, Tb, Eu, Rb, Bi, Se, As, Sc, Ag, Cd, Hf, Re, Au, Ac, Tc, Te and Rh At least one selected. As the metal complex dye, it is preferable to use a phthalocyanine-based dye or a ruthenium-based dye coordinated with a metal, and it is particularly preferable to use a ruthenium-based metal complex dye.

As the ruthenium-based metal complex dye, commercially available ruthenium-based metal complex dyes such as Ruthenium 535 dye, Ruthenium 535-bisTBA dye, and Ruthenium 620-1H3TBA dye manufactured by Solaronix can be used.

A co-adsorbent may be carried on the porous semiconductor layer 16A. Since the co-adsorbent is contained in the porous semiconductor layer 16A, the co-adsorbent suppresses association or aggregation of the sensitizing dye in the porous semiconductor layer 16A. The co-adsorbent can be appropriately selected from materials commonly used in the field according to the sensitizing dye to be combined.

The porous insulating layer 36A is formed on the porous semiconductor layer 16A so as to cover the entire porous semiconductor layer 16A. Porous insulating layer 36A is located between porous semiconductor layer 16A and counter conductive layer 28A and insulates the two layers. Furthermore, the porous insulating layer 36A is arranged to fill between the transparent conductive layer 14a and the transparent conductive layer 14b to insulate the two transparent conductive layers. The porous insulating layer 36A holds an electrolytic solution 42 containing a redox couple and a pyrazole compound. The porous insulating layer 36A further has insulating fine particles (second metal oxide particles) 36s and pores 36p.

The thickness of the porous insulating layer 36A laminated on the porous semiconductor layer 16A is preferably thinner than that of the porous semiconductor 16A. It is more preferable that the film thickness is as follows.

The electrolytic solution 42 mainly enters and is held in the pores 36p of the porous insulating layer 36A. The insulating fine particles 36s can be made of, for example, at least one selected from the group consisting of titanium oxide, niobium oxide, zirconium oxide, magnesium oxide, silicon oxide such as silica glass or soda glass, aluminum oxide, and barium titanate. . It is preferable to use insulating fine particles such as titanium oxide and zirconium oxide doped with Al or Mg. Furthermore, it is preferable to use rutile-type titanium oxide as the insulating fine particles 36s. When rutile-type titanium oxide is used for the insulating fine particles 36s, the average particle diameter of the rutile-type titanium oxide is preferably 5 nm or more and 500 nm or less, more preferably 10 nm or more and 300 nm or less.

It is preferable that the grooves of the scribe lines 60 are also filled with the insulating fine particles 36s. Thereby, the transparent conductive layer 14 a and the transparent conductive layer 14 b can be reliably insulated from each other on the substrate 12 .

The electrolyte solution 42 is not particularly limited as long as it is a liquid substance (liquid) containing an oxidation-reduction pair, and is a liquid substance that can be used in general batteries, dye-sensitized solar cells, and the like. Specifically, the electrolytic solution 42 is a liquid consisting of a redox couple and a solvent capable of dissolving it, a liquid consisting of a redox couple and a molten salt capable of dissolving it, or a liquid consisting of a redox couple and a solvent capable of dissolving it. It is a liquid made of molten salt and the like. Further, the electrolytic solution 42 may contain a gelling agent and be gelled.

Examples of redox couples include I ⁻ /I ₃ ⁻ system, Br ₂ ⁻ /Br ₃ ⁻ system, Fe ₂ ⁺ /Fe ₃ ⁺ system, quinone/hydroquinone system, and the like. More specifically, redox couples are metal iodides such as lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), calcium iodide (CaI ₂ ), and iodine (I ₂ ). In addition, the redox couple is a tetraalkylammonium salt such as tetraethylammonium iodide (TEAI), tetrapropylammonium iodide (TPAI), tetrabutylammonium iodide (TBAI), tetrahexylammonium iodide (THAI), and iodine can be in combination with Additionally, the redox couple may be a combination of a metal bromide such as lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), calcium bromide ( _CaBr2 ), and bromine. . As a redox pair, it is preferable to use a combination of LiI and I ₂ .

The redox couple solvent is selected from the group consisting of, for example, carbonate compounds such as ethylene carbonate and propylene carbonate, lactone compounds such as γ-butyl lactone and γ-valerolactone, and nitrile compounds such as 3-methoxypropionitrile and acetonitrile. is preferably a solvent containing at least one of When a pyrazole-based compound is added to the electrolytic solution 42, it is preferable to use a solvent with a dielectric constant of 20 or more and 80 or less, and it is particularly preferable to use γ-butyl lactone, which has a high dielectric constant, as the solvent.

The pyrazole compound is preferably a compound represented by the following general formula (1). wherein each R ¹ in the formula is independently selected from the group consisting of a hydrogen atom, a lower alkyl group, a halogen group, an amino group, a phenyl group, a furyl group, a methoxyphenyl group, a thienyl group, and a methylphenyl group; It is one of the All R ¹ in the formula may be the same group. Here, a lower alkyl group is defined as an alkyl group having 1 to 5 carbon atoms.

The pyrazole compound is, for example, pyrazole of general formula (2-1), 3-methylpyrazole of general formula (2-2) or 3,5-dimethylpyrazole of general formula (2-3) below. The molar concentration of the pyrazole-based compound in the electrolytic solution 42 is preferably 0.1M or more and 1.5M or less, more preferably 0.3M or more and 1.2M or less. If the molar concentration of the pyrazole-based compound in the electrolytic solution 42 exceeds 1.5M, the viscosity increases and the temperature of the porous insulating layer 36A tends to rise.

Many pyrazole-based compounds generally have high viscosity, so when a pyrazole-based compound is applied to a monolithic cell structure, there is concern that the electric resistance of the cell will increase (higher resistance).

According to the study of the present inventor, the average particle size of the insulating fine particles 36s is larger than the average particle size of the semiconductor fine particles 16s contained in the porous semiconductor layer 16A, and the porosity a of the porous insulating layer 36A is It is preferably larger than the porosity b of the porous semiconductor layer 16A. This relationship makes it possible to improve the resistance increase of the cell that may occur due to the addition of the pyrazole-based compound. Here, the porosity a is defined as the ratio of the volume of the pores 36p to the total area of the porous insulating layer 36A, and the porosity b is the ratio of the volume of the pores 16p to the total area of the porous semiconductor layer 16A. Defined as a percentage. It is particularly preferable that the average particle diameter of the insulating fine particles 36s is 100 μm or more and 500 μm or less.

The counter electrode conductive layer 28A is an electrode supported by the substrate 22 and serving as a counter electrode for the porous semiconductor layer 16A. A counter electrode conductive layer 28A is formed on the porous insulating layer 36A so as to cover the entire porous insulating layer 36A and to be electrically connected to the transparent conductive layer 14b on the substrate 12 . The counter electrode conductive layer 28A has, for example, carbon fine particles 28s and pores 28p.

Counter electrode conductive layer 28A may be formed from a conductive material and a catalytic material. As the material, for example, at least one selected from the group consisting of noble metal materials such as platinum and palladium, graphite, carbon black, ketjen black, carbon nanotubes, and carbon-based materials such as fullerene can be used.

The thickness of the counter electrode conductive layer 28A is, for example, 0.1 μm or more and 100.0 μm or less. Moreover, the specific surface area of the counter electrode conductive layer 28A is preferably, for example, 10 m ² /g or more and 200 m ² /g or less.

The DSC 100 can be manufactured by a known method, except for preparing and injecting an electrolytic solution 42 containing a pyrazole compound. For example, it can be produced by the method described in International Publication No. 2014/038570. For reference, the entire disclosure of WO2014/038570 is incorporated herein by reference.

According to the DSC of this embodiment, the porous insulating layer 36A and the counter electrode conductive layer 28A are laminated on the porous semiconductor layer 16A. Due to the monolithic cell structure, the positive charge appearing on the surface of the counter electrode conductive layer 28A is weakened by the porous insulating layer 36A, and the negatively charged pyrazole compound can be suppressed from being attracted to the counter electrode 28A side. . Moreover, in the porous insulating layer 36A formed of metal oxide, the pyrazole compound is easily adsorbed on the surface thereof, and is less likely to be attracted to the counter electrode 28A side. These effects improve uneven distribution of the pyrazole-based compound in the vicinity of the counter electrode 28A.

Experimental examples (Examples 1 to 5 and Comparative example 1) are shown below to describe the present disclosure in more detail. In the experiment, a dye-sensitized solar cell having the configuration of DSC100 was produced according to the production method described below.

<Example>
(1. Formation of monolithic laminate)
A commercially available titanium oxide paste (manufactured by Solaronix, trade name: Ti-Nanoxide D/SP, average particle diameter: 13 nm) was applied to a substrate (Nippon _Sheet Glass company) by the doctor blade method.

Next, the substrate coated with the titanium oxide paste was pre-dried at 100° C. for 30 minutes and then baked at 500° C. for 40 minutes. By repeating this process twice, a substrate having a titanium oxide film (thickness: 12 μm) was obtained as the porous semiconductor layer 16A.

Next, a dispersion liquid was prepared by adding ethanol to an aqueous dispersion liquid in which commercially available zirconium oxide particles (manufactured by Takiron C.I. Co., Ltd.) were dispersed. The solvent of this dispersion was replaced with terpineol, and the viscosity of the solvent was adjusted by mixing ethyl cellulose to produce a paste containing zirconium oxide powder. The paste was applied by a doctor blade method onto the substrate on which the titanium oxide film was formed.

Next, the substrate coated with the zirconium oxide powder-containing paste was pre-dried at 100° C. for 30 minutes, and then baked at 500° C. for 40 minutes. As a result, a substrate was obtained in which a zirconium oxide film (thickness: 6 μm) was formed on the porous semiconductor layer 16A as the porous insulating layer 36A.

Next, a platinum powder-containing paste prepared by dispersing platinum particles (manufactured by Furuya Metal Co., Ltd.) in terpineol was applied onto the substrate on which the zirconium oxide film was formed by a doctor blade method. After pre-drying the substrate coated with this paste at 100° C. for 30 minutes, it is fired at 500° C. for 30 minutes to form a monolithic type laminate in which a porous insulating layer 36A and a counter electrode conductive layer 28A are laminated on a porous semiconductor layer 16A. A substrate 12 having a laminate was obtained. The thickness of the counter electrode conductive layer 28A laminated on the porous insulating layer 36A was 0.1 μm.

(2, dye adsorption to laminate)
A dye adsorption solution having a concentration of 4×10 ⁻⁴ M was previously prepared by dissolving FSD19 dye in ethanol. The laminate was immersed in the dye adsorption solution at room temperature for 80 hours. After that, the laminate was washed with ethanol and dried at about 60° C. for about 5 minutes. Thus, the substrate 12 having the porous semiconductor layer 16A supporting the dye was obtained.

(3. Preparation of electrolytic solution)
3-Methoxypropionitrile (3MPL, manufactured by Aldrich) was added with 0.05M iodine (Aldrich), 0.8M dimethylpropylimidazole iodide (DMPII, Shikoku Kasei), and 0.05M dimethylpropylimidazole iodide (DMPII, manufactured by Shikoku Kasei). An electrolytic solution 42 containing a redox couple was prepared by dissolving 5M 3-methylpyrazole (manufactured by Aldrich).

(4. Injection of electrolytic solution)
An electrolytic solution 42 containing a redox couple was injected from the gaps of the cells, and the side surface of the cell in which the electrolytic solution 42 had permeated the laminate was sealed with a resin (TB03035B, manufactured by ThreeBond Co., Ltd.). Finally, each electrode was attached to a lead for IV measurement.

<Comparative example>
A dye-sensitized solar cell according to a comparative example has a sandwich-type cell structure shown in FIG. A dye-sensitized solar cell according to a comparative example was produced according to the production method described below.

(1. Formation of porous semiconductor layer)
First, a commercially available titanium oxide paste (manufactured by Solaronix, trade name: Ti-Nanoxide D/SP, average particle size: 13 nm) was applied to _a substrate (Nippon Sheet Glass company) by the doctor blade method.

Next, the substrate coated with the titanium oxide paste was pre-dried at 100° C. for 30 minutes and then baked at 500° C. for 40 minutes. By repeating this process twice, the substrate 12 on which a titanium oxide film (thickness: 12 μm) was formed as the porous semiconductor layer 16 was obtained.

A dye adsorption solution having a concentration of 4×10 ⁻⁴ M was previously prepared by dissolving FSD19 dye in ethanol. The laminate was immersed in the dye adsorption solution at room temperature for 80 hours. After that, the laminate was washed with ethanol and dried at about 60° C. for about 5 minutes. Thus, a substrate having the porous semiconductor layer 16 supporting the dye was obtained.

(2. Preparation of electrolytic solution)
3-Methoxypropionitrile (3MPL, manufactured by Aldrich) was added with 0.05M iodine (Aldrich), 0.8M dimethylpropylimidazole iodide (DMPII, Shikoku Kasei), and 0.05M dimethylpropylimidazole iodide (DMPII, manufactured by Shikoku Kasei). An electrolytic solution 42 containing a redox couple was prepared by dissolving 5M 3-methylpyrazole (manufactured by Aldrich).

(3. Formation of Counter Electrode Conductive Layer)
Using a vapor deposition device (model name: ei-5, manufactured by ULVAC), platinum was deposited at 0.1 Å/on a substrate 22 (manufactured by Nippon Sheet Glass Co., Ltd.) on which a fluorine-doped SnO ₂ film serving as the transparent conductive layer 24 was formed. s. The film thickness of the counter electrode conductive layer 28 is 0.1 μm.

(4. Injection of electrolytic solution)
The counter electrode conductive layer 28 and the porous semiconductor layer 16 are bonded together via a spacer to prevent a short circuit, and an electrolytic solution 42 containing a redox pair is injected into the gap between the counter electrode conductive layer 28 and the porous semiconductor layer 16. Then, the side surface of the cell filled with the electrolytic solution 42 was sealed with a resin (TB03035B, manufactured by ThreeBond Co., Ltd.). Finally, each electrode was attached to a lead for IV measurement.

In the experimental example, using a solar simulator, DSC under the standard conditions specified in the JIS standard (AM-1.5, simulated sunlight of 1 kW/m ² , surface temperature of 25 ° C., light incident direction perpendicular to the cell) A short-circuit current Jsc flowing through (light receiving area: 5 cm x 5 cm) was measured. After that, the DSC was left in a constant temperature bath at 85° C. for 500 hours according to the heat resistance test B-1, and the performance retention rate of the photoelectric conversion efficiency before and after the heat resistance test was determined.

A WACOM solar simulator was used for the measurement, and the irradiation energy was adjusted to 1 kW/m ² by a secondary reference solar cell. Each sample cell of Examples 1 to 5 and Comparative Example was placed in the center of the irradiation surface of the solar simulator, and an IV measurement system (manufactured by Sunrise: 6246SOL3) was connected to the positive and negative electrodes via lead wires to measure the performance. made an evaluation. In addition, the temperature in the constant temperature bath of SU-261 manufactured by Espec Co., Ltd. for the heat resistance test was set to 85 ° C., and the performance was evaluated using the IV measurement system after 500 hours after leaving each sample cell in the bath. did

The characteristics of each sample cell of Examples 1 to 5 and Comparative Example are shown below.

<Example 1>
Cell structure: monolithic type, insulating fine particles 36s contained in porous insulating layer 36A: zirconium oxide, pyrazole-based compound: 3-methylpyrazole, solvent for electrolytic solution 42: 3-methoxypropionitrile, counter electrode 28A: platinum <implementation Example 2>
Cell structure: monolithic type, insulating fine particles 36s contained in porous insulating layer 36A: titanium oxide (average particle size >400 nm), pyrazole-based compound: 3-methylpyrazole, solvent for electrolytic solution 42: 3-methoxypropionitrile , counter electrode 28A: platinum <Example 3>
Cell structure: monolithic type, insulating fine particles 36s contained in porous insulating layer 36A: zirconium oxide, pyrazole-based compound: 3-methylpyrazole, solvent for electrolytic solution 42: γ-butyl lactone, counter electrode 28A: platinum <Example 4 ＞
Cell structure: monolithic type, insulating fine particles 36s contained in porous insulating layer 36A: zirconium oxide, pyrazole-based compound: 3-methylpyrazole, solvent for electrolytic solution 42: 3-methoxypropionitrile, counter electrode 28A: carbon <implementation Example 5>
Cell structure: monolithic type, insulating fine particles 36s contained in porous insulating layer 36A: zirconium oxide and aluminum oxide, pyrazole-based compound: 3-methylpyrazole, solvent for electrolytic solution 42: 3-methoxypropionitrile, counter electrode 28A: Platinum <Comparative example>
Cell structure: sandwich type, insulating fine particles contained in porous insulating layer: not contained, pyrazole compound: 3-methylpyrazole, solvent for electrolytic solution 42: 3-methoxypropionitrile, counter electrode 28: platinum

Effective photoelectric conversion efficiencies A, B (%) and performance retention B/A (%) at the maximum output point obtained by IV measurement of each sample cell of Examples 1 to 5 and Comparative Example before and after the heat resistance test are shown. 1. As already explained, when the DSC is heated above about 80° C., the redox couple I ₃ ⁻ in the electrolyte is decomposed to produce I ₂ and I ⁻ . I ₂ is adsorbed on the surface of the porous semiconductor layer made of titanium oxide and becomes a current leak source, resulting in a decrease in the photoelectric conversion efficiency of the DSC. Certainly, compared with the measurement results obtained from the DSC of Examples 1 to 5, the performance retention rate of the comparative example shows a lower value.

In contrast, in the DSCs of Examples 1 to 5, the pyrazole-based compound permeating the entire laminate formed a complex with I ₂ , thereby suppressing the adsorption of I ₂ onto the titanium oxide surface. Become. The performance evaluation of Examples 1 to 5 was performed, and it was found that the reduction in the photoelectric conversion efficiency of the DSC after the heat resistance test was remarkably improved. By adopting a monolithic cell structure, the maximum performance retention after the heat resistance test reached 98%.

The performance retention obtained from the measurement of the sample cell of Example 2 is lower than the performance retention obtained from the measurement of the sample cell of Example 1. The reason for this is thought to be that titanium oxide particles with a large average particle size function as a porous insulating layer, but the proportion of _I2 adsorbed to the surface of the titanium oxide particles is higher than that of zirconium oxide particles. be done.

Features of the sample cell of Example 3 will be described in more detail. As a solvent for the electrolytic solution 42, γ-butyl lactone (GBL, manufactured by Kishida Chemical Co., Ltd., dielectric constant: 42), which is a high dielectric constant solvent, was used. Among Examples 1 to 3, the performance retention obtained from the measurement of the sample cell of Example 3 shows the highest value. By using γ-butyl lactone as the solvent for the electrolytic solution 42, the solubility of the pyrazole compound is dramatically improved. The pyrazole-based compound effectively contributes to the reaction with I ₂ , thereby appropriately suppressing the adsorption of I ₂ to titanium oxide.

It is preferable that the dielectric constant of the electrolytic solution 42 is 20 or more and 80 or less. When the dielectric constant is less than 20, the solubility of the pyrazole compound in solvents is reduced. Therefore, if the pyrazole-based compound is added excessively, it will exist as aggregates in the electrolytic solution, and there is a possibility that the reaction with I ₂ will not be effectively promoted when the DSC is heated.

Solvents such as ethylene carbonate, propylene carbonate and γ-valerolactone are also expected to dramatically improve the solubility of pyrazole compounds in addition to γ-butyllactone.

Features of the sample cell of Example 4 will be described in more detail. Carbon was used instead of platinum as the counter electrode conductive layer 28A. Specifically, a mixed powder of Ketjenblack and graphite (both manufactured by Nippon Graphite Co., Ltd.) is dispersed in a terpineol solution to generate a mixed powder-containing paste, and a zirconium oxide film is formed on a substrate with a doctor blade method. The paste was applied. After that, the substrate 12 coated with the solvent paste was pre-dried at 100° C. for 30 minutes, and then baked at 400° C. for 30 minutes.

Although carbon materials have electrical conductivity, their electrical conductivity is lower than that of metals, and their dielectric constant is also lower than that of metals. As a result, positive charges do not appear in the vicinity of the counter electrode, thereby suppressing the phenomenon in which the pyrazole-based compound is attracted to the counter electrode side, making it difficult for the pyrazole compound to be unevenly distributed on the counter electrode side. Therefore, the heat resistance of the cell is improved. In the measurement results, among Examples 1 to 5, the performance retention obtained from the measurement of the sample cell of Example 4 showed the highest value.

Features of the sample cell of Example 5 will be described in more detail. A mixed layer of zirconium oxide and aluminum oxide was used as the porous insulating layer 36A instead of zirconium oxide. In other words, the insulating fine particles 36s contained in the porous insulating layer 36A contain mixed particles of zirconium oxide and aluminum oxide. The mass ratio of zirconium oxide and aluminum oxide is 93:7.

From the measurement results of the experimental example, it can be seen that the performance retention obtained from the measurement of the sample cell of Example 5 is good. From this result, it is preferable that the insulating fine particles 36s contained in the porous insulating layer 36A contain two or more kinds of metal oxide particles having different valences. In other words, the insulating fine particles 36s preferably contain a metal oxide with a first valence and a metal oxide with a second valence lower than the first valence. An example of a pentavalent metal oxide is niobium oxide, an example of a tetravalent metal oxide is zirconium oxide or titanium oxide, an example of a trivalent metal oxide is aluminum oxide, a divalent metal oxide An example of a substance is magnesium oxide.

It is particularly preferred that the first valence metal oxide is tetravalent zirconium oxide and the second valence metal oxide is a divalent or trivalent metal oxide. For example, the second valence metal oxide is trivalent aluminum oxide or magnesium oxide.

When metal oxide particles with different valences are in contact with each other, oxygen vacancies, that is, positively charged holes, are generated in the metal oxide particles with a high valence at the contact interface. Therefore, the negatively charged pyrazole-based compound is attracted to the porous insulating layer 36A, and as a result, it is possible to suppress the omnipresent distribution of the pyrazole-based compound in the vicinity of the counter electrode.

It is preferable that the porous insulating layer 36A contains more metal oxide particles with a higher valence (first valence) than metal oxide particles with a lower valence (second valence). . For example, the insulating fine particles 36s contained in the porous insulating layer 36A may contain mixed particles of zirconium oxide and aluminum oxide, and the porous insulating layer 36A may contain more zirconium oxide particles than aluminum oxide particles. The mass ratio of the high-valence metal oxide particles and the low-valence metal oxide particles contained in the entire insulating fine particles 36s is preferably 80:20 or more and 99:1 or less. Also, the average particle size of the metal oxide particles with a high valence is different from the average particle size of the metal oxide particles with a low valence. The average particle size of the metal oxide particles with a higher valence is preferably larger than the average particle size of the metal oxide particles with a lower valence. For example, the average particle size of the metal oxide particles with high valence is preferably 100 μm or more and 500 μm or less, and the average particle size of the metal oxide particles with low valence is preferably 20 μm or more and 200 μm or less.

[Description of Incorporation]
This application claims priority based on Japanese Patent Application No. 2019-137939 filed on July 26, 2019, and the entire disclosure of this application is incorporated herein by reference.

Claims (16)

a first electrode having a porous semiconductor layer containing first metal oxide particles and supporting a dye;
a second electrode serving as a counter electrode to the first electrode;
A porous insulating layer provided between the first electrode and the second electrode, the porous insulating layer holding an electrolytic solution containing a redox couple and a pyrazole-based compound and containing second metal oxide particles. layer and
with
The average particle size of the second metal oxide particles is larger than the average particle size of the first metal oxide particles, and the porosity of the porous insulating layer is larger than the porosity of the porous semiconductor layer. , dye-sensitized solar cells. The pyrazole compound is represented by the following general formula,

Here, each R ¹ in the formula is independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen group, an amino group, a phenyl group, a furyl group, a methoxyphenyl group, a thienyl group, and a methylphenyl 2. The dye-sensitized solar cell according to claim 1, which is one selected from the group consisting of groups and may be the same group. 3. The dye-sensitized solar cell according to claim 1 , wherein the molar concentration of said pyrazole compound in said electrolytic solution is 0.3M or more and 1.2M or less. The dye-sensitized solar cell according to any one of claims 1 to 3 , wherein the electrolytic solution contains a solvent having a dielectric constant of 20 or more and 80 or less. 5. The dye-sensitized solar cell according to claim 4 , wherein the solvent contains at least one selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyllactone, and γ-valerolactone. 6. The dye-sensitized solar cell according to any one of claims 1 to 5 , wherein said second electrode has a counter electrode conductive layer containing carbon fine particles. 7. The dye booster according to any one of claims 1 to 6 , wherein the second metal oxide particles contain at least one selected from the group consisting of zirconium oxide, titanium oxide, niobium oxide, aluminum oxide, and magnesium oxide. Sensitive solar cell. The dye-sensitized solar cell according to any one of claims 1 to 6 , wherein the second metal oxide particles contain two or more kinds of metal oxide particles having different valences. 7. The second metal oxide particles according to any one of claims 1 to 6 , including metal oxide particles of a first valence and metal oxide particles of a second valence lower than the first valence. Dye-sensitized solar cell. 10. The dye-sensitized solar cell according to claim 9 , wherein the average particle size of the first valence metal oxide particles is larger than the average particle size of the second valence metal oxide particles. 11. The dye booster according to claim 9 or 10 , wherein said first valence metal oxide particles are zirconium oxide and said second valence metal oxide particles are divalent or trivalent metal oxide particles. Sensitive solar cell. 12. The dye-sensitized solar cell of claim 11 , wherein the second valence metal oxide particles are aluminum oxide or magnesium oxide. The mass ratio of the first valence metal oxide particles and the second valence metal oxide particles contained in the entire second metal oxide particles is 80:20 or more and 99:1 or less. The dye-sensitized solar cell according to claim 9 . further comprising a transparent substrate supporting the first electrode;
A first transparent conductive layer is formed on the transparent substrate, and a second transparent conductive layer is formed on the transparent substrate electrically isolated from the first transparent conductive layer,
14. The porous semiconductor layer of the first electrode is formed on the first transparent conductive layer, and the second electrode is electrically connected to the second transparent conductive layer. 2. The dye-sensitized solar cell according to claim 1. The dye-sensitized solar cell according to any one of claims 1 to 14 , wherein said porous insulating layer has a thickness smaller than that of said porous semiconductor layer. The dye-sensitized solar cell according to any one of claims 1 to 14 , wherein said porous insulating layer has a thickness of 0.2 µm or more and 20 µm or less.

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